Germany's Langer shot a 66 while Couples had a 64 to set up a final round showdown between the two former US Masters winners.
Langer is seven under on 203 after three rounds with Peter Fowler a stroke behind Couples.
"I'm just happy to be in the hunt with 18 holes to play," said Langer, winner of the title in 2010. "There's a lot of guys in with a chance, so I know I'll have to shoot one of the lower scores to win."
Couples said: "It was a very, very good day. Once I got going I didn't miss many shots. I hit my irons solid and when I hit them close I made the putt."
Englishman Barry Lane (66) is tied for fourth heading into the final round, on three-under with Americans John Cook (66) and overnight leader Gary Hallberg (73).